Minor display issues on new beta "commit details" page

<!-- Thank you for reporting an issue. Please make sure that your style is up to date and you checked the recent commits to ensure that your issue wasn't recently addressed. If the page is not publicly accessible, include the HTML code around the issue. --> GitHub has introduced a new "commit details" page, currently in public beta: https://github.com/orgs/community/discussions/139005 The style seems to mostly work on this page, but has some small differences vs the old view which would be nice to keep consistent. * **Browser**: Firefox 130.0 (64-bit) * **Operating System**: macOS 14.6.1 * **Link to page with the issue**: I think any commit should do, for example my screenshots are from https://github.com/tornadoweb/tornado/commit/a6dfd70d7a6398b2187021df63ca77daa5781e5e * **Screenshot**: New commit details page (`Feature Preview > New Commit Details Page > Enable`):  Old commit page (`Feature Preview > New Commit Details Page > Disable`):  The main differences I noticed: - Code background is transparent / same as page background. This is the most jarring thing for me. - Header background color changed (github default seems to just be same color as background?) - Some visual artifacts around each file header — background color extended too far / not far enough? There may be some other subtle differences, but maybe not worth spending too much effort on, in case there are further changes to the commit details view — but if the code background could be made non-transparent I think that would be a huge help for readability, especially with a custom / patterned background is configured.